Always whiten your teeth prior to having any type of restoration replaced, including bonding. None of the materials which we employ to restore your teeth will bleach. So, if you want your teeth to be lighter, you need to whiten first and have the restoration replaced once the whitening is completed in order to match it to the lightened shade of your teeth.
I use Rely-X Luting plus cement every day in my practice. It is a wonderful product with a proven track record. I would not hesitate to have all-zirconium crowns cemented with this product.
A calcified root canal is one of the most difficult situations to treat in regards to root canal therapy. It sounds as if you have two of them in one tooth. If one canal was previously treated (and the other two were left untreated), the chances of successfully treating the other two canals is poor. You may want to consider the alternative of extracting the tooth in question and replacing it with a dental implant and crown or a bridge.
The cavity occurrance rate during Invisalign or ClearCorrect treatments is completely controlled by the patient. It is imperative that you do not eat or drink anything other than water with the trays in your mouth. Otherwise, you will be more susceptible to cavities. I instruct my patients to remove their aligners prior to eating or drinking anything other than water. If the patient cannot brush following a meal or snack, I recommend leaving the aligners out of the mouth until proper brushing and flossing can be done.
The composite veneers should be completely removed if they are to be replaced with porcelain veneers. The teeth will be protected with provisional or 'temporary' veneers while the porcelain veneers are fabricated. These temporaries will seal and protect your teeth during the interim, and they should prevent any sensitivity issues.
